What you need to know are all the facts about the results of operations with even and odd numbers. They are: even + even = even even + odd = odd odd + odd = even even - even = even even - odd = odd odd - even = odd odd - odd = even even × even = even even × odd = even odd × odd = odd You have here a case of this: (odd + odd) - (even + even) = We can replace "(odd + odd)" by "even" and have this: even - (even + even) = And we can replace "(even + even)" by "even" and have this: even - even = Then we can replace "even - even" by "even", and we end up with this: even So the answer has to be an even number. Of the choices you have, which are a)45 b)54 c)35 d)53 only "b)54" is an even number. So that is the only possible choice. There are lots of possibilities of that resulting in 54. For instance, here are some: (11 + 65) - (10 + 12) = 54 (67 + 29) - (28 + 14) = 54 (47 + 79) - (20 + 52) = 54 (99 + 97) - (98 + 44) = 54 Edwin